Implementation of micro-ball nanodiamond anvils

Since invention of the diamond anvil cell technique in the late 1950s for studying materials at extreme conditions, the maximum static pressure generated so far at room temperature was reported to be about 400 GPa. Here we show that use of micro-semi-balls made of nanodiamond as second-stage anvils in conventional diamond anvil cells drastically extends the achievable pressure range in static compression experiments to above 600 GPa. Micro-anvils (10–50 μm in diameter) of superhard nanodiamond (with a grain size below ~50 nm) were synthesized in a large volume press using a newly developed technique. In our pilot experiments on rhenium and gold we have studied the equation of state of rhenium at pressures up to 640 GPa and demonstrated the feasibility and crucial necessity of the in situ ultra high-pressure measurements for accurate determination of material properties at extreme conditions.

An NCD micro-ball of ~12 μm in diameter was compressed in a DAC in a Ne pressure transmitting medium (a schematic diagram is shown in insert in the upper right corner). Continues line is a result of fitting the experimental data (black dots; error bars are within the symbol size) up to 38 GPa with the third-order BM3 equation of state (K300=489(5) GPa, K′=3.2(2), V0=3.393(1) cm3 mol−1). At pressures above 40 GPa the NCD seems to become more compressible, but the observed effect is simply a consequence of bridging of the micro-ball between the DAC’s anvils and the development of the deviatoric stresses in it. Insert in the bottom left shows as synthesized NCD balls (10–50 μm in diameter) in a sodium chloride medium. The scale bar is 100 μm.